Willis Lamm's
Traffic Signal Collection

  Traffic Signal Lenses

Many early traffic signals designs were based on railroad signal technology however early on traffic signal designers discovered a significant difference between railroad and highway signals. Railroad signals were aimed down a specific and somewhat narrow track. They needed to project a fairly weak light source a long distance in a specific direction. Traffic signals had to be easily visible from a much wider angle by traffic and pedestrians. Therefore the Fresnel lenses used by the railroads were found to be inadequate for highway use.

A number of ideas and patents evolved that projected light straight out, but also down and to the sides. Frosted and "orange peel" lenses tended to cause "phantoms" (appear to be lit when not lit) when struck by low angle sunlight. Manufacturers experimented with a variety of lens, reflector and visor patterns. Lenses evolved into the "small bead" lenses used in modern day signals.

The beads on the inside of the lenses are typically made relatively flat on the bottom to trap light from the reflector but to minimize reflected sunlight. Therefore it was critical that lenses be installed correctly and most of them have "TOP" cast in tiny letters at the top of the lens, lest a signal maintenance person might have a "senior moment" while replacing a lens.

Early lenses also came in lettered (command) and non-lettered configurations. Early signals were not standardized and it was a while until all areas of the country had electric traffic signals. Therefore many communities opted to have "commands" displayed on signal lenses to minimize confusion by unfamiliar drivers.

This section illustrates a variety of different lens types and their applications.

Click on any image to bring up a larger view on a new page.

Orange peel lenses

These lenses were so named due to the orange peel texture on the inside of the lens. Orange peel provided a smooth illumination of the lens which was advantageous in lettered lenses as the letters didn't appear distorted due to the effect that beads had on projected light. Orange peel lenses came in both lettered and non lettered configurations. One weakness of orange peel lenses was their tendency to produce phantoms when hit directly by early morning or late afternoon sunlight.


Crosshatch lenses

These lenses had a faint crosshatch pattern on the inside of the lens to diffuse light. The crosshatch also provided a smooth illumination of the lens which was advantageous in lettered lenses as the letters didn't appear distorted due to the effect that beads had on projected light. Crosshatch lenses came in both lettered and non lettered configurations. Crosshatch lenses also tended to produce phantoms when hit directly by early morning or late afternoon sunlight.

Here is another style of crosshatch lettered lens found in some early W.S. Darley signals among others. Some of the lenses, such as made by Corning and MacBeth-Evans were designed for the letters to be painted. Others displayed the lettering more discretely through changes in the surface of the glass.
Corning painted letters,


Holophane Ribbed Lenses

A number of early lenses were pretty flat and had vertical ribs to control lateral diffusion of lens light. This design worked pretty well for post mounted signals but ribbed lenses in span wired signals tended to have phantom problems.

This particular lens was manufactured for early Essco signals.


Adler Bar Lenses

In 1934 inventor Charles Adler, Jr. patented a series of traffic lenses designed for the colorblind. These lenses displayed bars that clarified the signal's indication. A vertical bar indicated "go." A diagonal bar indicated "caution." A horizontal bar indicated "stop." As early drivers became more familiar with traffic signals the need for lettered and bar lenses diminished, however a small number can still be seen in older signals in some communities.

Here is a more complete feature on the Adler Bar Lens.


Holophane Spider Web Lenses

GE had Holophane produce an interesting lens that was composed of a dozens of tiny ribs that loosely resembled a spider web. These lenses naturally got the nickname, spider web lenses. Spider webs could be found in Novalux and early groove back and 4-way signals. In the 1940s GE switched to brick pattern lenses.

Siemens continued to produce spider web lenses for European signals and the Siemens lenses are virtually identical to the original Holophanes.


Holophane Spider Web Commands

GE Holophane lenses also came with command lettering. These lenses had the larger spiderweb ribs however the command lenses had a smooth frosted surface between the spiderweb ribs rather than the micro ribs that were in the regular Holophane lenses. The idea here was to produce a less harsh light that displayed the letters more clearly.

(The distortion in the "O" is from the camera angle viewing the letter through the GE logo in the glass.)


Continue to Part Two

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